Hongchun Liu

Background: The Braak hypothesis proposes that α-synuclein (α-syn) pathology may originate in the gastrointestinal tract and propagate to the central nervous system along the gut–brain axis; however, the precise propagation routes and the factors influencing this process remain controversial. Methods: A gut-originating Parkinson’s disease model was established by injecting α-syn preformed fibrils (PFF) into the duodenal muscularis of C57BL/6J and A53T transgenic mice. Phosphorylated α-synuclein (p-α-syn) pathology, motor behavior, and gut microbiota were assessed, with truncal vagotomy included to evaluate its association with gut-to-brain propagation. Results: In C57BL/6J mice, at 4 months post-injection, p-α-syn deposition was observed in both the duodenal muscular layer and the striatum, accompanied by gut microbiota alterations and motor behavioral deficits. Truncal vagotomy was associated with reduced p-α-syn levels in the brain and alterations in the gut microbiota. In A53T transgenic mice, p-α-syn pathology and neurodegenerative changes were also observed following α-syn PFF injection, though the lack of a genetically matched wild-type control precludes definitive attribution of these phenotypes solely to the A53T transgene. Conclusions: These results align with the Braak hypothesis, showing that gut-derived p-α-syn pathology and associated functional impairments are intimately linked to vagal pathways during their propagation to the brain. Additionally, this gut-origin PD mouse model may serve as a useful tool for future mechanistic investigations.

Depression is increasingly linked to microbiota–gut–brain axis dysfunction, yet current monoaminergic antidepressants show limited efficacy. This study investigated the therapeutic potential and underlying mechanisms of GV-971, a marine-derived oligosaccharide, in a chronic restraint stress (CRS) mouse model. We first established that 8 h of daily restraint for 4–8 weeks induces a stable depression-like phenotype characterized by behavioral despair and significant reduction in peripheral monoamine neurotransmitters (5-HT and norepinephrine). GV-971 treatment robustly attenuated CRS-induced depression- and anxiety-like behaviors, restored hippocampal serotonin levels, reduced elevated plasma corticosterone concentrations, and ameliorated CRS-induced adrenal cortical hyperplasia. Mechanistically, GV-971 significantly suppressed neuroinflammation by inhibiting microglial hyperactivation in the prefrontal cortex and hippocampus. Concurrently, it repaired intestinal barrier dysfunction, evidenced by reduced permeability, restored mucosal integrity, and recovered goblet cell numbers. Crucially, integrated shot-gun metagenomics and plasma metabolomics revealed that GV-971 not only reshaped microbial taxonomy but also functionally recalibrated the gut ecosystem. It enriched beneficial taxa (e.g., Bifidobacterium pseudolongum, Bacteroides uniformis) and specific metabolic pathways, leading to increased short-chain fatty acids (valeric and caproic acids) and a significant reduction in plasma levels of tryptophan–kynurenine pathway metabolites, specifically the neurotoxic compounds kynurenine and quinolinic acid. Fecal microbiota transplantation (FMT) from GV-971-treated donors partially recapitulated the antidepressant and gut-protective effects in CRS recipients, confirming a causal role for the remodeled microbiota. Collectively, GV-971 exerts antidepressant effects by coordinately remodeling the gut microbiota, normalizing tryptophan and SCFA metabolism, restoring gut barrier integrity, and dampening central neuroinflammation, supporting its potential as a novel gut–brain axis-targeted therapy for depression.

Parkinson’s disease (PD) is pathologically characterized by the abnormal aggregation of α-synuclein and the progressive loss of dopaminergic neurons, with microglia-mediated neuroinflammation acting as a pivotal driver of pathogenesis. Ferroptosis, an iron-dependent form of regulated cell death, significantly contributes to PD progression. However, the precise mechanisms governing microglial ferroptosis under α-synuclein pathology, particularly the regulatory role of the master antioxidant transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), remain elusive. Here, we employed an in vitro BV2 microglial model and an in vivo A53T transgenic mouse model to elucidate the regulatory effects and underlying mechanisms of Nrf2 on ferroptosis-associated phenotypes induced by α-synuclein pre-formed fibrils (PFFs). In vitro, PFF treatment significantly downregulated microglial Nrf2 expression, triggering ferroptosis-associated phenotypes characterized by reactive oxygen species (ROS) accumulation, ferrous iron (Fe²⁺) overload, and elevated lipid peroxidation. Genetic knockdown of Nrf2 exacerbated these ferroptosis-associated phenotypes and accelerated α-synuclein aggregation. Conversely, Nrf2 overexpression or pharmacological activation via dimethyl fumarate (DMF) profoundly suppressed α-synuclein pathology and mitigated ferroptosis-associated signatures. In vivo, microglial activation in the substantia nigra of PD mice was accompanied by marked Nrf2 downregulation. Strikingly, microglia-specific Nrf2 overexpression significantly reversed motor and non-motor deficits (including olfactory and locomotor impairments), demonstrating the sufficiency of microglial protection. Furthermore, systemic administration of the Nrf2 activator DMF not only ameliorated motor dysfunction but also concurrently rescued nigral dopaminergic neurons and reduced striatal α-synuclein aggregation. Taken together, our findings identify Nrf2 downregulation-driven microglial ferroptosis-associated phenotypes as a critical pathogenic mechanism, and demonstrate that targeting this pathway in vivo ameliorates motor and non-motor deficits while preserving dopaminergic neurons in PD mice. These findings support further research on Nrf2 activation and DMF as potential therapeutic strategies for PD.

Main observation and conclusion: As part of our continuing efforts toward the discovery of the biologically active diterpenoids from medicinal plants, six new C‐ring aromatized abietane diterpenoids, clerodenoids A—F (1—6), were isolated from Clerodendrum chinense. These C‐ring aromatized compounds mainly belonged to the rearranged abietane skeletons of 17(15→16)‐abeo‐abietane (2—4) and 17(15→16), 18(4→3)‐diabeo‐abietane (5 and 6). Their structures were elucidated by extensive spectroscopic data, X‐ray crystallography, and ECD calculation. Compounds 5 and 6 displayed strong antiproliferative activities against A549 and HL‐60 cell lines.